Vibration excited sound absorber

Abstract

A vibration excited sound absorber for reducing the sound radiation from a vibrating surface. Each sound absorber has a radiating element which is connected to the vibrating surface by a coupling means. The vibrating surface is partially covered with one or more devices. The dynamic response of the sound absorber is tuned so that the volume velocity of the radiating element is substantially equal in amplitude but opposite in phase relative to the volume velocity of the surrounding exposed vibrating surface. The net volume velocity of the surface is thereby reduced.

What is claimed is:  
     
       1. A vibration excited sound absorber for reducing the sound radiated from a region of a vibrating surface, said region having an area S, and said sound absorber comprising: 
       a sound radiating element defining a sound radiating surface and  
       a coupling element comprising a member having:  
       a first surface attachable to a first part of the region of the vibrating surface such that a second part of the region with area S′ remains exposed; and  
       a second surface attached to the sound radiating element;  
       said coupling element being operable to couple motion of the region of the vibrating surface to said sound radiating element, so that the sound radiating element is excited into motion by vibration of the region of the vibrating surface;  
       wherein the dynamic response of said sound absorber is tuned so that velocity u of the first part of the region of the vibrating surface causes the sound radiating surface to vibrate with a volume velocity of approximately −S′×u at one or more frequencies.  
     
     
       2. A sound absorber as in  claim 1 , in which said radiating element forms part of an acoustically sealed volume. 
     
     
       3. A sound absorber as in  claim 2  in which said vibrating surface forms one side of said acoustically sealed volume. 
     
     
       4. A sound absorber as in  claim 1  and including means for attaching said sound absorber to said vibrating surface. 
     
     
       5. A sound absorber as in  claim 1  in which said radiating element is solid and substantially rigid. 
     
     
       6. A sound absorber as in  claim 1  in which said radiating element is a fluid mass supported by a fluid spring. 
     
     
       7. A sound absorber as in  claim 1  in which said coupling element includes at least one spring. 
     
     
       8. A sound absorber as in  claim 1  in which said coupling element has multiple degrees of freedom and said sound absorber is tuned to vibrate with a volume velocity of approximately −S′×u at each of a plurality of frequencies. 
     
     
       9. A sound absorber as in  claim 1  wherein said coupling element member comprises: 
       a housing for attaching the coupling element to said vibrating surface; and  
       an acoustical seal coupling said housing to said radiating element,  
       wherein said housing, said acoustic seal and said radiating element form an acoustically sealed volume.  
     
     
       10. A sound absorber as in  claim 1  further comprises: 
       one or more spacing elements attached to the first surface of said coupling element member operable to attach the sound absorber to the vibrating surface such that the sound absorber is spaced from the vibrating surface, allowing fluid circulation between the vibrating surface and the sound absorber.  
     
     
       11. A sound absorber as in  claim 1  comprising a plurality of sound radiating elements and coupling elements tuned to vibrate with a volume velocity of approximately −S′×u at a plurality of frequencies. 
     
     
       12. A sound absorber as in  claim 1 , further comprising a magnet operable to attach the sound absorber to the vibrating surface. 
     
     
       13. A sound absorber for reducing the sound radiated from a region of a vibrating surface, said region having an area S, and said sound absorber comprising: 
       a sound radiating element with a sound radiating surface positioned in close proximity to or embedded in said vibrating surface and  
       a coupling means coupled to the vibrating surface on one side and to the sound radiating surface on another side, said coupling menas being operable to couple motion of the vibrating surface to the motion of said radiating element,  
       wherein the dynamic response of said sound absorber to said motion of the vibrating surface is tuned so that the volume velocity of said radiating velocity of the corresponding region of the vibrating surface at at least one frequency, and  
       wherein the sound radiating surface of said radiating element is oriented away from said vibrating surface and the ratio of the amplitude of the motion of the radiating element to the amplitude of the motion of the vibrating surface is −S′/A, where S′=S−A and A is the area of the radiating element, and A is less than S.  
     
     
       14. A sound absorber for reducing the sound radiated from a region of a vibrating surface, said region having an area S, and said sound absorber comprising: 
       a sound radiating element with a sound radiating surface positioned in close proximity to or embedded in said vibrating surface; and  
       a coupling means coupled to the vibrating surface on one side and to the sound radiating surface on another side, said coupling means being operable to couple motion of the vibrating surface to the motion of said radiating element,  
       wherein the dynamic response of said sound absorber to said motion of the vibrating surface is tuned so that the volume velocity of said radiating element is substantially equal in amplitude but opposite in phase to the volume velocity of the corresponding region of the vibrating surface at at least one frequency, and  
       wherein the sound radiating surface of said radiating element is oriented towards said vibrating surface and in which the ratio of the motion of the radiating element to the motion of the vibrating surface is −S′/A, where S′=S+A and A is the area of the radiating element, and A is less than S.  
     
     
       15. A method for reducing the sound radiated from a vibrating surface, comprising the steps of: 
       dividing said surface into a number of contiguous first regions;  
       determining the volume velocity of each first region and thereby determining a number of second regions which significantly contribute to the radiated sound; and  
       attaching a sound absorber to each said number of second regions, said sound absorber comprising a radiating element and a coupling element, the coupling element having first and second surfaces and being attached to the vibrating surface on the first surface and to the radiating element on the second surface and causing the vibration of said second region to be transmitted to said radiating element,  
       wherein said sound absorbers are configured so that a change in volume of the sound absorber is proportional in amplitude but substantially opposite in phase to a displacement of the first surface of the coupling element in a direction normal to the vibrating surface to which the sound absorber is attached.  
     
     
       16. A method for reducing the sound radiated from a vibrating surface, comprising the steps of: 
       determining the dimensions of said vibrating surface;  
       computing from said dimensions a set of attachment positions on said vibrating surface;  
       attaching a sound absorber at each attachment position of said set of attachment positions, said sound absorber comprising a radiating element and a coupling element, the coupling element having first and second surfaces and being attached to the vibrating surface on the first surface and to the radiating element on the second surface and causing the vibration of the vibrating surface at each attachment position to be transmitted to said radiating element; and  
       tuning each said sound absorber so that the radiating element produces a volume velocity proportional equal in amplitude but substantially opposite in phase to the velocity of the first surface of the coupling element in a direction normal to the vibrating surface.  
     
     
       17. A vibration excited sound absorber for reducing the sound radiated from a region of vibrating surface, said region having an area S and said sound absorber comprising: 
       a body having a sound radiating surface and a coupling surface for attaching the body to a first part of the region of the vibration surface and leaving a second part of the region with area S′ exposed,  
       wherein said sound absorber is tuned such that a velocity u of the coupling surface in a direction normal to the region of the vibrating surface causes the sound absorber to generate a volume velocity of approximately −S′×u.  
     
     
       18. A vibration excited sound absorber in accordance with  claim 17 , wherein said body comprises: 
       a compliant coupling element providing said coupling surface and a portion of said radiating surface; and  
       a substantially rigid element providing a portion of said radiating element.  
     
     
       19. A vibration excited sound absorber in accordance with  claim 18 , wherein said compliant coupling element includes at least one of the bellows coupling, an air-spring, a coil spring, a wave spring, a leaf spring, a solid elastomer, an elastomer with fluid-filled voids, a magnetic spring and an electromagnetic spring. 
     
     
       20. A method for reducing the sound radiated from a vibrating surface, comprising the steps of: 
       determining the dimensions of said vibrating surface;  
       computing from said dimensions a set of contiguous regions of said vibrating surface; and  
       for each region of the set of contiguous regions:  
       attaching a sound absorber to a first part of the region such that a second part of the region with area S′ is exposed, said sound absorber comprising a body having a sound radiating surface and a coupling surface for attaching the body to the first part of the region of the vibrating surface; and  
       tuning said sound absorber such that a velocity u of the coupling surface in a direction normal to the region of the vibrating surface causes the sound absorber to generate a volume velocity of approximately −S′×u.  
     
     
       21. A method for reducing the sound radiated from a vibrating surface, comprising the steps of: 
       dividing said surface into a set of contiguous regions of said vibrating surface; and  
       determining the volume velocity of each of the set of contiguous regions and thereby determining a subset of regions which significantly contribute to the radiated sound;  
       for each region of the subset of regions:  
       attaching a sound absorber to a first part of the region such that a second part of the region with area S′ is exposed, said sound absorber comprising a body having a sound radiating surface and a coupling surface for attaching the body to the first part of the region of the vibration surface; and  
       tuning said sound absorber such that a velocity u of the coupling surface in a direction normal to the region causes the sound absorber to generate a volume velocity of approximately −S′×u.  
     
     
       22. A vibration excited sound absorber for reducing sound radiated from a region of a vibrating surface, said sound absorber comprising: 
       a compliant layer defining a first surface and second surface, said first surface attachable to said region of the vibrating surface;  
       a substanially rigid plate having a first side attached to the second surface of said compliant layer and a second side; and  
       a sound absorber body attached to the second side of said substantially rigid plate and leaving an area S′ of the second side of said substantially rigid plate exposed,  
       wherein said sound absorber body is tuned such that a velocity u of said substantially rigid plate in direction normal to the second side of the substantially rigid plate causes the sound absorber body to generate a volume velocity of approximately −S′×u.  
     
     
       23. A vibration excited sound absorber as in  claim 22 , wherein said compliant layer includes an air spring.